Solution: At this moment, how deep is the water in the bigger tank?

Problem Statement: EE Board April 1996

Two vertical conical tanks are joined at the vertices by a pipe. Initially the bigger tank is full of water. The pipe valve is open to allow the water to flow to the smaller tank until it is full. At this moment, how deep is the water in the bigger tank? The bigger tank has a diameter of 6 ft and a height of 10 ft, the smaller tank has a diameter of 6 ft and a height of 8 feet. Neglect the volume of water in the pipeline.